by USA TODAY, USA TODAY

by USA TODAY, USA TODAY

Roman Catholic Church law requires cardinals, the pope's chief advisers, to elect his successor. There are 208 cardinals from 68 nations but only those under age 80 are eligible to vote.

How many cardinals enter the Sistine Chapel to choose the next pope depends on how quickly the conclave is called. Currently 118 are eligible but by the time of the pope's resignation, Feb. 28, Cardinal Lubomyr Husar of the Ukrainian Catholic Church will have turned 80. Crossing the line very quickly after that are Cardinal Walter Kasper of Germany, whose 80th birthday is March 5, and Cardinal Severino Poleto of Italy, whose birthday is March 18.

Of the current 118 electors, most (67) were named by Benedict XVI and the rest (51) by Pope John Paul II.

Although the USA has only 6% of the 1.2 billion global Catholic population, it has 19 cardinals including 11 electors, about 10% of the total electors.

Electors by region:

Europe, 62

North America, 17

South America, 13

Africa, 11

Asia, 11

Central America, 3

Oceania, 1

Countries with the most cardinal-electors:

Italy: 28

United States: 11

Germany: 6

Brazil, India, Spain: 5 each

France, Poland: 4 each

U.S. electors (year named)

Raymond Burke, (2010) archbishop emeritus of St. Louis, now head of the Vatican's high court, the Apostolic Signatura

Daniel DiNardo, (2007) archbishop of Galveston-Houston

Timothy Dolan, (2012) archbishop of New York, president of the U.S. Conference of Catholic Bishops

Francis George, (1998) archbishop of Chicago

James Harvey, (2012) of Milwaukee, former head of the papal household and now archpriest of a major basilica in Rome

William Levada, (2006) archbishop emeritus of San Francisco, retired after heading the Congregation for the Doctrine of the Faith